Process for cold-in-place recycling using foamed asphalt and lubrication additive

ABSTRACT

Cold-in-place asphalt recycling is disclosed. A foamed asphalt may be produced by injecting water and optionally compressed air into a hot asphalt stream. A lubricating surfactant may be added to the hot asphalt stream to improve performance. The foamed asphalt may be mixed with reclaimed material to provide a uniformly coated paving material that can compacted to a desired density.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application No. 61/086,331 filed on Aug. 5, 2008, entitled “LUBRICATION ADDITIVE AND PROCESS FOR THE PRODUCTION OF COLD IN PLACE RECYCLING USING FOAMED ASPHALT,” which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosure pertains to asphalt processing and more particularly to cold-in-place asphalt recycling.

BACKGROUND

Cold-in-place recycling, commonly referred to as CIR, is a process where an existing bituminous pavement or a combination of bituminous pavement and untreated aggregate are milled or ground from a pavement surface to a depth of up to 6 inches, combined with a virgin bituminous material, mixed, and repaved without removal of the materials from the existing grade.

SUMMARY

The invention is directed to improved processes for cold-in-place recycling of asphalt. In one embodiment, the invention is a cold-in-place recycling method in which an ethoxylated diamine surfactant and water are mixed with an asphalt binder to form a foamed composition of the surfactant and asphalt. The foamed composition of the surfactant and asphalt is mixed with milled recycled pavement to provide a uniformly coated paving material that can be compacted to a desired density.

In another embodiment, the invention is a foamed cold-in-place recycling method in which a foamed asphalt binder is produced by injecting one or more of water and a compressed air stream into a liquid asphalt stream that includes a lubricating surfactant. The foamed asphalt binder is combined with bituminous material in a continuous mixing process to produce a recycled bituminous mix. The recycled bituminous mix is conveyed into a paver and is then paved onto an existing grade.

In another embodiment, the invention is a foamed cold-in-place recycling method in which a foamed asphalt binder is produced by combining water and a lubricating surfactant into a liquid asphalt stream. The foamed asphalt binder is combined with bituminous material in a continuous mixing process to produce a recycled bituminous mix. The recycled bituminous mix is conveyed into a paver and is then paved onto an existing grade.

While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the detailed description is to be regarded as illustrative in nature and not restrictive.

DETAILED DESCRIPTION

The invention pertains to improved CIR processes in which a lubricating additive is added to a foaming asphalt binder. This provides better coating, easier construction, improved compaction, and reduced processing temperatures. One indication of improved coating is the richer color of the paving material, as the more uniform the coating, the darker the color. The duller, browner color of conventional CIR foamed mix is observed when all of the particles are not coated. A firmer mat is also an indication that the binder is coated or more uniformly spread over all the particles rather than having small globules of asphalt interspersed among the fine aggregate particles.

CIR Recycling

CIR recycling is a process in which an existing bituminous pavement or a combination of bituminous pavement and untreated aggregate are milled or ground from a pavement surface to a depth of several inches, combined with a foamed asphalt material, mixed, and repaved. In some embodiments, CIR recycling involves a train method in which a number of pieces of equipment are arranged, in order, to accomplish each of these tasks on site.

For example, in a train method, a milling machine may be positioned at the front of the line to mill existing pavement down a desired depth. A hammer mill crusher may be located behind the milling machine, or “downstream” with respect to the flow of materials, such that the hammer mill crusher (or another type of mill or crusher) receives the milled bituminous material from the milling machine. A pug mill may be located downstream of the hammer mill crusher to mix the milled and crushed material with a foamed asphalt binder in a continuous process. A tanker or other truck holding hot asphalt may be disposed between the hammer mill crusher and the pug mill.

Once the material has been mixed, it can be deposited on the road and transferred to a paver using a pickup machine. In some cases, the material can be dumped from the pug mill directly into the paver. The paver lays the mix and the mix is then rolled or compacted. In some cases, it has been determined that it is beneficial to drop the mix from the pug mill onto the grade and let the pickup machine transfer it to the paver as this can reduce or eliminate frequent stopping and starting of the paver.

In another process, a reclaimer is used to rip up or chew up the pavement. The removed material is tilled or reclaimed (sometimes virgin aggregate is added) and foamed asphalt is sprayed onto the reclaimed mix, which is then deposited behind the reclaimer. In some cases, a grader is used to shape the finished mix for thickness and slope. In some instances, the material as deposited is compacted without shaping. This process produces a recycled mix that is suitable for correcting poor grades, adding depth to the compacted layer (when using additional aggregate) and generally obtaining a water shedding surface on which additional layers of hot mix asphalt can be placed.

In another process, a stationary foaming mixing system can be used in combination with milled material that is collected on site and brought back to a central mixing location. This process can be used to produce a cold mix that can be either grader or paver laid to produced a hard, water shedding surface on which to add a chip seal or an overlay. In each of these processes, a lubricating surfactant can be used in the foaming process.

Foaming Process

In some embodiments, a foamed asphalt binder is beneficial to the CIR process. A foamed asphalt binder can be produced using several different techniques. In one technique, a foamed asphalt binder is formed by injecting a small amount of water and compressed air into a very hot stream of asphalt binder which causes the asphalt binder to foam when the water/asphalt blend is sprayed onto the milled bituminous material. In this process, about 1 to 5 weight percent water is injected into virgin asphalt binder along with vigorous mixing of the components to create a foam. The resultant mix that is placed develops strength very quickly because of the relatively low level of water added to the asphalt binder to make the foam and because of the relatively rapid loss of water through evaporation caused by the heat of the asphalt.

In another technique, a foam is produced from an emulsion that includes about 60 to 70 weight percent asphalt binder and about 30-40 weight percent water combined at a temperature in a range of about 30° C. to 60° C. Use of an emulsion can result in effectively coating the milled material at or near about 100 percent level.

In some cases, quicker setting emulsions impart a chemical “break” to the emulsion which enables the emulsion to coat the milled material and then chemically bond the asphalt particles to the aggregate material and cause the water to break or separate from the asphalt. There can be a noticeably faster cure imparted to the emulsion system compared to conventional slow setting or medium setting emulsion mixed blends.

In some embodiments, lubricating surfactants can be added to the asphalt binder or to the water injected into the asphalt binder to enhance foaming and to lubricate and enhance spreading of the asphalt binder onto milled material particles. Consequently, recycled bituminous materials can be produced that provide rapid strength development while also providing about or up to 100 percent coating of particles and also provide the desired appearance and density. In some cases, the lubricating effect provided by the lubricating surfactants can prevent or substantially reduce the tendency of some foamed CIR mixtures to stick to the paver screed. Moreover, while foamed CIR may be performed using binders at approximately 360° F., the use of lubricating, foam enhancing additives can result in the reduction of the temperature needed for construction by as much as 60° F.

In some embodiments, a foamed asphalt binder can be produced by injecting water and compressed air, along with one or more lubricating surfactants, into a stream of hot asphalt. The hot asphalt stream may be a virgin asphalt such as PG 52-34 binder. In some cases, the lubricating surfactant is added to the asphalt prior to injecting the water and compressed air. In some instances, the lubricating surfactant is added to the water prior to injection of the water. In some embodiments, the hot asphalt is flowing through a pipe or other structure, the water is injected into the hot asphalt stream via a first nozzle and the compressed air is injected into the hot asphalt stream via a second nozzle. In some cases, foaming may occur with injection of water in the absence of injection of compressed air.

Asphalt Binder

A variety of different asphalt binders are commercially available. As an example, several different asphalt binders are commercially available from a variety of sources. Non-limiting examples of asphalt binders are PG 52-34, PG 58-34, PG 64-28, PG 70-28, PG 76-28, PG 70-22 and PG 76-22. A particular asphalt binder is PG 52-34, which has an absolute viscosity (measured at 140° F.) of 540 Poise, a penetration (at 77° F.) of 236 dmm and a specific gravity (at 60° F.) of 1.03.

Lubricating Surfactants

A variety of lubricating surfactants can be used in producing foamed asphalt binders. Examples of suitable lubricating surfactants include naturally occurring compounds and more commonly synthesized chemical compounds from three categories of surfactants: detergents, wetting agents and emulsifiers. Surfactants can be specifically categorized as being anionic, cationic, amphoteric and nonionic.

Suitable anionic surfactants include but are not limited to fatty acids (saturated and unsaturated fatty acids), fatty acid pitch (stearic acid pitch), fatty acid derivatives (fatty acid esters and fatty acid sulfonates), and organo phosphates (alkyl phosphates).

Suitable cationic surfactants include, but are not limited to, alkyl amines, alkyl quaternary ammonium salts, heterocyclic quaternary ammonium salts, amido amines, and non-nitrogenous sulfur or phosphorous derivatives.

Suitable amphoteric surfactants, which include an anionic molecular portion and a cationic molecular portion, include but are not limited to amino acids, amino acid derivatives, betain derivatives (alkylbetains and alkylaminobetains), imidazolines, and imidazoline derivatives.

Suitable nonionic surfactants include, but are not limited to, fatty acid ester bonds (SPANS and TWEENS), with surfactant ether bonds (alkylphenolpolyoxyethylenes and polyoxyethylenated alcohols), surfactants with amid bonds (alkanolamides, mono and diethanolamides and their derivatives), alkylenated oxide copolymers and polyoxyethylenated mercaptans.

Other surfactants and non-surfactant additives can be found in U.S. patent application Ser. No. 11/871,782, filed Oct. 12, 2007 entitled WARM MIX ASPHALT BINDER COMPOSITIONS CONTAINING LUBRICATING ADDITIVES, which application is hereby incorporated by reference herein in its entirety.

In some embodiments, the lubricating surfactant is an ethoxylated diamine. An illustrative but non-limiting example of a suitable ethoxylated diamine is DT-3, or tris(2-hydroxyethyl)-N-tallow-alkyl-1,3-diaminopropane. In some embodiments, about 0.5 weight percent DT-3 can be used in the asphalt binder.

Compositions

In some embodiments, a foamed asphalt may be produced by injecting about 0.5 to 5 weight percent water and about 0.05 to about 3 weight percent of an ethoxylated diamine surfactant into a liquid asphalt stream. The liquid asphalt stream may be an asphalt binder such as PG 52-34. In some embodiments, compressed air at a pressure of about 20 to about 50 psi may also be injected into the liquid asphalt stream to enhance foaming. In some embodiments, during the foaming process, the liquid asphalt stream is at a temperature in the range of about 300° F. to about 380° F. In some cases, the liquid asphalt stream is at a temperature in the range of about 320° F. to about 360° F.

The resulting foamed asphalt may be combined with milled bituminous material (either on site or at a central location) at a rate of about 0.5 to 4 percent foamed asphalt binder by weight of milled bituminous material. This material, once laid and compacted, can achieve a density, measured two days after compaction, of at least about 88 to about 95 percent of the theoretical maximum density of the mix being placed.

Example One

A trial run was conducted using the “train method” of cold-in-place recycling. A PR1000T Caterpillar milling machine was used to mill the existing pavement approximately 3.5 inches deep. A portable 3033 Cedar Rapids hammer mill crusher with a double screen deck was used to size the milled material to 1 inch and smaller size. A portable Barber Green pugmill with a twin shaft approximately 10 feet long was used to mix the milled material with the foamed asphalt binder. The foaming process was conducted using a Soter spray bar to inject water into the asphalt stream just prior to introduction of the asphalt into the milled material. After mixing the milled material with the foamed asphalt, the mix was placed in a windrow behind the pugmill and a pickup machine was used to transfer the mix to a paver which then laid the mix. A screed on the paver provided initial compaction and final compaction of the mix was accomplished with pneumatic and steel wheeled rollers.

The asphalt binder used was a PG 52-34 at a nominal temperature of 360° F. The asphalt was delivered to the project in a tanker and transferred to smaller tank designed to straddle the windrow and so move down the paving project as the entire milling and mixing train operates on the project. One to two percent water is added at the milling head to cool the head and keep down dust and another 1-2% water is added during the crushing phase of the operation. This water is in addition to the water injected at the spray head to produce the foamed asphalt. The ambient temperature on this project was 70° F. A total of 1.65% virgin 52-34 binder by weight was added to the milled material. For this test 0.5% DT-3 ethoxylated diamine lubricating additive was added by weight to the PG 52-34 binder.

At the spray bar in the mixing chamber the mixture color was a darker richer looking color compared to comparable runs performed without the lubricating additive. The mix was more workable in the windrow and picked up easily for transfer to the paver. There was good flow through the paver, flights and under the screed. The coating was uniform and darker in color than the same mix produced without the lubricating additive. The mat behind the paver was firmer than the comparable untreated mix. The mix rolled well and mat appeared firmer under the roller. There was an obvious color difference between the conventional foamed CIR mix and the CIR mix produced with the lubricating additive. Cores were taken from both the conventional and test sections 2 days after construction. These cores were tested for density. The average density of 5 cores in the conventional section was 127.3 lbs/ft3. The average density for 4 cores taken in the section produced with the lubricating additive was 129.0 lbs/ft³.

Example Two

Another trial run was conducted using the “train method” of cold-in-place recycling. A portion of the existing pavement was milled, crushed and mixed with a foamed asphalt binder.

The foaming process was conducted by injecting water into the asphalt stream just prior to introduction of the asphalt into the milled material. After mixing the milled material with the foamed asphalt, the mix was transferred to a paver which then laid the mix. A screed on the paver provided initial compaction and final compaction of the mix was accomplished with pneumatic and steel wheeled rollers.

The asphalt binder used was a PG 52-34 at a nominal temperature of 360° F. The asphalt was delivered to the project in a tanker and transferred to smaller tank designed to straddle the windrow and so move down the paving project as the entire milling and mixing train operates on the project. One to two percent water is added at the milling head to cool the head and keep down dust and another 1-2% water is added during the crushing phase of the operation. This water is in addition to the water injected at the spray head to produce the foamed asphalt.

By mid-morning, as the pavement and air temperatures increased, it was found that the asphalt mix developed a tendency to stick to the screed as a result of the fines and binder increasing in viscosity. An attempt was made to resolve the problem by reducing the binder content from 1.2 or 1.3 gallons per foot to 0.8 gallons per foot. It was found that this reduced but did not eliminate the problem. Moreover, this resulted in a less-than-optimal binder content. It was found that by adding 0.3 weight percent of DT-3 to the binder, the binder content could be kept at 1.2 gallons per foot while eliminating the mix sticking problem.

Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. Although the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the above described features. 

The following is claimed:
 1. A cold-in-place asphalt recycling method, which method comprises: milling an existing pavement surface to a desired depth to provide milled bituminous material on-site; combining the milled bituminous material with a foamed asphalt binder formed from a lubricating cationic surfactant in an amount of about 0.05 to about 3 weight percent of the foamed asphalt binder, water, and liquid asphalt binder heated to a temperature sufficient to produce the foamed asphalt binder, to produce a paving material on-site; and compacting the paving material on-site to provide a recycled pavement surface.
 2. The method of claim 1, wherein the recycled paving surface has a density, measured two days after compacting, of at least about 88 percent of the theoretical maximum density.
 3. The method of claim 1, comprising combining virgin aggregate and the milled bituminous material with the foamed asphalt binder.
 4. The method of claim 1, comprising combining the milled bituminous material with the foamed asphalt binder in an amount of about 0.5 to 4 percent asphalt binder by weight of milled bituminous material.
 5. The method of claim 1, further comprising adding the lubricating cationic surfactant to the heated liquid asphalt binder prior to forming the foamed asphalt binder.
 6. The method of claim 1, further comprising adding the lubricating cationic surfactant to the water prior to forming the foamed asphalt binder.
 7. The method of claim 1, further comprising separately adding the lubricating cationic surfactant and water to the heated asphalt binder prior to forming the foamed asphalt binder.
 8. The method of claim 1, further comprising adding compressed air to the heated liquid asphalt binder.
 9. The method of claim 1, wherein the lubricating cationic surfactant comprises an alkyl amine, alkyl quaternary ammonium salt, heterocyclic quaternary ammonium salt, amido amine or non-nitrogenous sulfur or phosphorous derivative.
 10. The method of claim 1, wherein the lubricating cationic surfactant is an ethoxylated diamine.
 11. The method of claim 1, wherein the foamed asphalt binder is formed from about 0.5 to about 5 weight percent water and about 0.05 to about 3 weight percent lubricating cationic ethoxylated diamine surfactant with the balance being heated liquid asphalt binder.
 12. The method of claim 1, comprising laying the paving material using a paver.
 13. The method of claim 1, comprising laying the paving material using a grader.
 14. The method of claim 1, wherein the heated liquid asphalt binder is at a temperature greater than 300° F.
 15. The method of claim 1, wherein the foamed asphalt binder produces a uniformly coated paving material.
 16. A cold-in-place asphalt recycling method to prepare a recycled asphalt pavement surface, which method comprises: producing a foamed asphalt binder by combining about 0.5 to about 5 weight percent water and about 0.05 to about 3 weight percent lubricating cationic surfactant, and optionally compressed air, with a liquid asphalt binder heated to a temperature greater than about 300° F. to provide a foamed asphalt binder; in a continuous mixing process, milling an existing pavement surface to provide milled bituminous material and combining the foamed asphalt binder with the milled bituminous material to produce a recycled bituminous mix; conveying the recycled bituminous mix into a paver; laying the recycled bituminous mix onto an existing grade; and compacting the recycled bituminous mix to form a recycled asphalt pavement surface.
 17. The method of claim 16 further comprising adding the lubricating cationic surfactant to the liquid asphalt binder prior to producing the foamed asphalt binder.
 18. The method of claim 16, comprising combining virgin aggregate and the milled bituminous material with the foamed asphalt binder.
 19. The method of claim 16, further comprising crushing the milled bituminous material.
 20. The method of claim 16, further comprising placing a hot mix asphalt layer on the recycled asphalt pavement surface. 